When using a twin-screw extruder, pay attention to its […]
When using a twin-screw extruder, pay attention to its principles, that is, structural principles, temperature principles, and deceleration principles, which can help you operate it better. In addition, in order to improve its performance, it is necessary to master some operating skills, such as adding heat insulation gaskets between the feeding section and the flange of the second section, which is conducive to improving its operating efficiency.
What are the principles of twin screw extruder?
1. Structural principles
For the basic mechanism of the extrusion process, in simple terms, a screw rotates in the barrel and pushes the plastic forward. The screw structure is an inclined surface or slope wound on the center layer, the purpose of which is to increase the pressure in order to overcome the greater resistance.
2. Temperature principle
First of all, the weighbridge feed preheating and the barrel/mold heater may work and are very important at startup. In addition, the motor inputs energy, that is, the frictional heat generated in the barrel when the motor overcomes the resistance of the viscous melt to rotate the screw. The more important heat source for all plastics.
3. The principle of deceleration
In most extruders, the screw speed is changed by adjusting the motor speed. The drive motor usually rotates at a full speed of about 1750 rpm, which is too fast for an extruder screw. If it is rotated at such a fast speed, too much frictional heat will be generated and a uniform melt cannot be prepared.
What are the tips to improve the performance of twin screw extruders?
1. Add heat insulation gaskets between the feeding section and the flange of the second section
The feeding section of the barrel is mostly water-cooled, and is locked with the second section of the barrel (heating) by a flange, and the heat can be continuously conducted from the high-temperature barrel to the cold barrel. As a result, the second-stage cylinder cannot maintain a sufficient temperature. Usually, the operator sets a temperature of 180°C in the second section of the cylinder.
2. Replace the extruder cooling system with a high-pressure cooling system
As we all know, turbulent flow in a pump can cause more heat exchange on the tube wall than laminar flow. Turbulence in high-pressure transmission has a high degree of lateral momentum exchange, which breaks the boundary layer. As a result, the violent fluid movement causes a large amount of heat exchange between the tube wall and the fluid.
3. Use appropriate modifications to increase the feed volume
Side feeding is usually used to feed the filler into the twin screw extruder. Many processors need to make very high filling amounts of fillers, which often have a very low bulk density. The filling volume is restricted by the following factors: the volumetric feeding capacity of the side feed and the volumetric feeding capacity of the main screw of the extruder.